Internal combustion engines, including diesel engines, gasoline engines, and natural gas burning engines, create and emit a variety of different pollutants during operation that may be harmful to the environment and to human and animal health. These air pollutants can include, for example, oxides of nitrogen such as NO2 and NO3, commonly referred to as NOx. Due to increased environmental awareness, including government mandated emissions regulations and control, many manufacturers of internal combustion engines have taken measures to reduce the amount or effect of the pollutants that are created. Some of these measures are incorporated into the exhaust system associated with the internal combustion engine to remove, trap or chemically react with the pollutants being exhausted from the engine.
One type of exhaust treatment measure that reduces NO through a chemical reaction is known as Selective Catalytic Reduction, commonly referred to as SCR. In the SCR process, a gaseous or liquid reductant agent is introduced to the exhaust system where the reductant agent can intermix with the exhaust gasses or it can be absorbed onto a catalyst located in the exhaust system downstream of the internal combustion engine. A common reductant agent is urea, though other suitable substances such as ammonia may be readily used in an SCR process. The NO pollutants can react with the reductant agent and the catalyst such that the NO is converted into environmentally benign nitrogen (N2) and water (H2O).
The reductant agent is often stored in a storage tank that is located proximate to the internal combustion engine. For example, when the internal combustion engine is employed to power a vehicular machine, the storage tank will typically be included as part of the machine. A fluid line may be in fluid communication with the storage tank and the exhaust system to convey the fluid reductant agent to the exhaust system where the reductant agent can be introduced upstream of the catalyst or, in other embodiments, injected onto the catalyst.
Because the internal combustion engine may be used in an extremely cold environment, accommodations must be employed to ensure that the fluid reductant agent does not freeze within the storage tank or the fluid line during operation of the engine. For example, urea typically freezes at 11° C. and if the engine is shut off for prolonged periods in a cold environment, it may be frozen when the engine is next started. An adverse consequence of this scenario is that the SCR system cannot adequately communicate the frozen reductant agent from the storage tank and introduce it into the exhaust system to convert the NON.
One method of addressing the problems associated with frozen reductant agent in an SCR system is described in U.S. Patent Application Publication No. 2009/0205320 (the '320 application). The '320 publication describes an SCR system having three different heating components placed in three different locations throughout the system. The heating components include an electrical resistance heater disposed in the storage tank for the reductant agent, an engine coolant line passing through the storage tank, and an electric resistance heater proximate to the reductant agent supply line. The '320 application also discloses a control strategy for activating and deactivating the various heating components. However, the control strategy is designed for controlling three distinct heating components and relies on measuring the exact temperature of the reductant agent. Moreover, the disclosed control strategy does not appear to include error-checking strategies to help ensure that the reductant agent is in the appropriate physical state.
The present disclosure is directed at overcoming one or more of the deficiencies set forth above and/or other problems present in the prior art.